The objective of this proposal is to study the kinetics of granule cell maturation and its relation to the specific association of granule cells with astroglia in developing mouse cerebellum. The final mitosis of proliferative granule cells will be established by pulse labeling with 3H-thymidine. After defined time periods, cerebellar cells will be plated in micro cultures and the association of heavily labeled, postmitotic granule cells with astroglia will be visualized by staining the cultures with antibody raised against glial filament protein and then carrying out autoradiography. The result of the in vitro studies will be verified in vivo. The influence of the weaver glia on the kinetics of granule cell maturation and specific association with astroglia will be assessed by labeling them with 3H-thymidine and then co-culturing them with +/+ astroglia in reaggregate cultures under conditions where the only glial process out-growth will originate from +/+ glia. The distribution of successive generations of granule cells in the internal granule layer will be analyzed in vivo by double labeling with 3H-thymidine followed by 14C-thymidine. This method will allow us to evaluate whether successive generations form layers or other spatial compartments according to their precise time of origin.